Integrated circuit package with sensor and method of making

ABSTRACT

An integrated circuit (“IC”) package comprising an IC die having a top surface and a bottom surface, an elongate member having opposite first and second end portions and a mid portion. The mid portion is positioned proximate the top surface of the IC die. The IC package also includes an encapsulant block having a top surface, a bottom surface and opposite first and second lateral side surfaces. The encapsulant block encapsulates the IC die and the elongate member. Either or both of the first and second end portions of the elongate member are exposed.

BACKGROUND

This application is a Divisional of and claims priority to U.S. patentapplication Ser. No. 14/723,122, filed May 27, 2015. Saki application isincorporated herein by reference in its entirety.

Integrated circuit (“IC”) packages typically include an integratedcircuit die that is mounted on and electrically attached to a leadframe.The electrical connections between the die and leadframe are often madeby wire bonding in which a thin conductor wire is bonded at one end to acontact on the die and at the other end to a lead of the leadframe. Theleadframe, die and bond wires are usually encapsulated in a protective,nonconductive block of material, such as epoxy. Portions of theleadframe are exposed through the bottom wall and/or sidewalls of theencapsulating block to enable electrical connection of the die to otherelectronics and/or to facilitate the transfer of heat from the IC die tothe surrounding environment.

In an integrated circuit sensor package the die in the package is asensor die that is adapted to sense a physical parameter of thesurroundings of the IC sensor package. For example in a capacitive typehumidity sensor a thin polymer film is attached to a surface of an ICdie and is connected to electrical circuitry within the die. Changes inhumidity affect the amount of moisture absorbed by the polymer film.Moisture absorption causes a change in the capacitance of the film. Thischange in capacitance is measured by the die circuitry and isrepresentative of the humidity of the air. To make such an IC sensorpackage, the polymer film attached to the die must be exposed to thesurrounding air.

SUMMARY

An integrated circuit (“IC”) package including an IC die having a topsurface and a bottom surface and an elongate member having oppositefirst and second end portions and a mid portion. The mid portion of theelongate member is positioned proximate the top surface of the IC die.The IC package includes an encapsulant block having a top surface, abottom surface and opposite first and second lateral side surfaces. Theencapsulant block encapsulates the IC die and the elongate member. Atleast one of the first and second end portions of the elongate member isexposed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric top view of a prior art integrated circuit sensorpackage.

FIG. 2 is an isometric bottom view of the integrated circuit sensorpackage of FIG. 1.

FIG. 3 is a cross-sectional view of a mold assembly in use to producethe integrated circuit sensor package of FIG. 1 and FIG. 2.

FIG. 4 is an isometric side view of an example embodiment of anintegrated circuit sensor package.

FIG. 5 is an isometric top view of the integrated circuit sensor packageof FIG. 4.

FIG. 6 is a bottom plan view of the integrated circuit sensor package ofFIGS. 4 and 5.

FIG. 7 is an isometric top view of a production assembly including aportion of a lead frame strip with integrated circuit dies mounted onintegrally connected lead frame portions of the leadframe strip.

FIG. 8 is an isometric top view of a production assembly like FIG. 7,but further including tubular members engaging the integrated circuitdies.

FIG. 9 is a top isometric view of the production assembly of FIG. 8after molding.

FIG. 10 is an isometric bottom view of one of the tubular members shownin FIG. 9,

FIG. 11 is an isometric top view of another example embodiment of anintegrated circuit sensor package.

FIG. 12 is an end view of an example embodiment of a tubular memberhaving a rectangular cross section.

FIG. 13 is an isometric view of an integrally connected array of tubularmembers.

FIG. 14 is a flow diagram of a method of making an integrated circuitsensor package

FIG. 15 is a flow diagram of a method of determining the value of aparameter of atmospheric air with an encapsulated integrated circuitsensor assembly.

DETAILED DESCRIPTION

FIGS. 1 and 2 are top and bottom isometric views of a prior artintegrated circuit (“IC”) package 10. The IC package 10 includes agenerally rectangular box-shaped block 12 of encapsulant, which may bemold compound. The encapsulant block 12 has a top portion 14 and anopposite bottom portion 16. The top portion 14 has a central hole 18therein, which exposes a top surface portion 22 of an IC die 20. The ICdie 20 is mounted on top of a lead frame 30 having a die pad 32 andleads 34. The bottom surfaces of the die pad 32 and leads 34 are exposedat the bottom surface 16 of the encapsulant block 12.

FIG. 3 is a cross-sectional elevation view of a mold assembly 11 used toproduce the integrated circuit package 10 of FIGS. 1 and 2. FIG. 3 showswhat will become the IC package 10, prior to its singulation fromadjacent identical IC package units. As shown by FIG. 3, the die pad 32and leads 34 of the lead frame 30 are supported on a top surface of abottom mold platen 54 (sometimes referred to in the art as a “molddie”). The IC die 20 is mounted on a top surface of the die pad 32 byattachment medium 42 such as solder or adhesive. Bond wires 44 attachedelectrical contact pads 26 on a top surface 22 of the IC died 22 toleadframe leads 34.

A top mold platen 52 has a hole 62 extending upwardly from a bottomsurface thereof. This hole 62 receives a reciprocal plunger member 56therein. A spring 58 biases plunger member 56 in a downward direction.When the top mold platen 52 is closed, as illustrated in FIG. 3, theplunger member 56 engages a top surface of the die 20 and remainsengaged with it as long as the top platen 52 remains closed.

Prior to closing the top platen member 52, a release film 64 isstretched over the bottom surface thereof. When the mold assembly 11 isin the operating position illustrated in FIG. 3, mold compound 15 isinjected into a mold cavity 13 formed between the top and bottom platens52, 54. The plunger member 56 prevents mold compound 15 from enteringthe space directly above a central, sensor element portion 21 of the die20, ultimately forming the hole 18, shown in FIG. 1, above the sensorelement 21. The mold compound 15 cools to form the encapsulant block 12.At this point, the top platen 52 is opened and an IC package 10, such asillustrated in FIGS. 1 and 2, is removed. The hole 18 functions toexpose the sensing element 21 to air. The hole 18 also enables efficientheat transfer from the sensor die 20 to the surrounding environment.

Such IC sensor packages 10 are relatively expensive to produce. A newmold assembly 11 must be produced for each different IC package designconfiguration due to the fact that the plunger member 56 must havefootprint and location corresponding to that of the sensor element 21.Another sensor die configuration, in which the sensor element is largerand/or at a different location on the top surface of the die, would,thus requires a different top platen. Mold assemblies 11 are extremelyexpensive. Thus a requirement to provide a unique mold assembly 11 foreach different die sensor package configuration would considerablyincrease the overall cost of producing the sensor packages. There is nosuch requirement for conventional IC packages that do not have sensordies that must be exposed to the atmosphere. A single mold assembly canbe used to produce many different IC package configurations.

Another problem with IC sensor die packages such as IC package 10 isthat, because the hole 18 is positioned at the top of the package, itallows dust to collect on the top surface of the sensor element 21 thatreduces contact between the sensor element 21 and the atmosphere. Thedust can cause inaccuracies in the output of the sensor die 20.

FIG. 4 is an isometric side view of an example embodiment of a newintegrated circuit package 100. FIG. 5 is a top isometric view and FIG.6 is a bottom plan view of the integrated circuit package 100. In theillustrated embodiment, the IC package 100 is a quad flat no-leadspackage (“QFN”). As shown by FIGS. 4 and 5, the IC package 100 includesan IC die 102 having electrical contact pads 104 on a top surfacethereof. An attachment medium 106, such as solder or an adhesivematerial, attaches a bottom surface of the IC die 102 to a leadframe112.

The leadframe 112 includes a die pad 116 having an exposed bottomsurface 118, as shown in FIG. 6. The leadframe 112 also includes aplurality of leads 120. Each lead 120 has a severed side surface 123 anda bottom surface 125 that are exposed through a lateral sidewall and abottom wall of an encapsulating block of mold compound 150.

Bond wires 124 (only one shown) connect the contact pads 104 on the topsurface of the IC die 102 to leads 120, FIGS. 4 and 5.

As shown in FIGS. 4 and 5, a tubular member 130 has a first end portion132 with a first end opening 134 and a second end portion 136 with asecond end opening 138. A cylindrical passage 139 extends between thetwo openings 134, 136. The tubular member 130 has a mid portion 140 thathas a hole 142 therein. The hole 142 has a central axis extendingperpendicular to the central longitudinal axis of the cylindricalpassage 139. The tubular member 130 may have a small flat portion 145 onits circumference that engages the top surface of the IC die 102. Thehole 142 is formed on this flat portion 145, as best shown in FIG. 4.(This flat surface is also shown in FIG. 10 on a tubular member that hasnot yet been singulated.) The block 150 of mold compound may be agenerally rectangular box-shaped block with flat lateral side surfacesextending between generally flat top and bottom surfaces. The first end132 of the tubular member 130 terminates flush with one lateral sidesurface 151 of the mold compound block 150 and the second end 136terminates flush with the opposite lateral side surface 153 of theencapsulant block. The mid portion 140 of the tubular member rests on atop surface 101 of the IC die 102 above a sensing element 141 on the topsurface 101 of the die. The hole 142 is positioned in the flat portion145 of the tubular member that is above the sensing element 141.

The tubular member 130 and hole 142 therein thus allow the ambientatmosphere, or other gases, to come into contact with the sensor element141 on the top surface 104 of the IC die 102. Different types of sensorelements 141 are provided for different types of sensors, for examplehumidity sensors and gas sensors.

FIGS. 7-9 illustrate various stages in the production of integratedcircuit packages 100. FIG. 7 illustrates a lead frame strip 170 thatincludes a plurality of integrally connected lead frames 112. An IC die102 is mounted on a die pad 116 of each lead frame 112, by attachmentmedia 106, such as solder or adhesive. A 2×3 leadframe portion of aleadframe strip 170 is illustrated in FIGS. 7-9. It will be understoodthat the leadframe strip 170 may comprise various leadframe gridconfigurations. In one embodiment, wire bonding, during which bond wires124 (FIGS. 4 and 5, not shown in FIGS. 7-9) are connected at oppositeends thereof to IC die contacts 104 and leadframe leads 120, isperformed at this stage. Bond wires 124, shown in FIGS. 4 and 5, are notshown in FIGS. 7-9 to avoid clutter.

In FIG. 8, elongate tubular members 131 have open ends and aresufficiently long to extend over all the dies 102 in one row of the leadframe strip 170. The tubular members 131 are held in engagement witheach of the dies 102 by an attachment medium such as solder or adhesive.In another embodiment the tubular members 131 are held in the positionshown by a vacuum 176 that is applied at the open ends of the tubularmembers 131. In this embodiment, holes 140, 142, are provided in eachtubular member 131 at positions so that the holes 140, 142 will belocated over sensing elements 141 in corresponding IC dies 102, as shownin FIG. 8. (This vacuum is held until molding takes place.)

FIG. 12 illustrates an example embodiment of a tubular member 180. Inthis embodiment the tubular member has a rectangular tubular wall 182defining a rectangular fluid passage 164 therethrough. The flat bottomsurface of the tubular wall may facilitate mounting of the tubularmember on respective dies. The tubular member 180 contains a holepositionable over each associated die, like the holes 142, 144 providedin the bottom surface of the tubular member 170, FIG. 10. Therectangular tubular member 180 may be mounted and singulated, etc., likethe tubular member 170 as described below.

Next, as illustrated in FIG. 9, the entire lead frame strip 170 andattached components are molded to form an unsingulated mold compoundslab 152 around the leadframe strip 170, dies 102 and tubular members131. This slab 152 is then singulated along saw streets AA, BB, CC andDD, as by conventional singulation means, such as singulation saws orstealth lasers. This singulation separates the assembly shown in FIG. 9into individual IC packages 100 as illustrated in FIGS. 4-6.

FIG. 11 is an isometric top view of another example embodiment of anintegrated circuit sensor package 200. In the illustrated embodiment ofFIG. 11, the IC sensor package 200 is a quad flat no-leads package(“QFN”). The IC sensor package 200 includes an IC die 202 havingelectrical contact pads 204 on a top surface thereof. An attachmentmedium (not shown), such as solder or an adhesive material, attaches abottom surface of the IC die 202 to a leadframe 212.

The leadframe 212 includes a die pad 216 having an exposed bottomsurface, which may be identical to surface 118 of die pad 116, as shownin FIG. 6. The leadframe 212 also includes a plurality of leads 220.Each lead 220 has an exposed severed side surface 223. Each lead 220also has an exposed bottom surface 225, which may be identical to thebottom surfaces 125 of leads 120 shown in FIG. 6. The severed sidesurfaces 223 and bottom surfaces 225 of the leads 220 are exposedthrough an encapsulating block of mold compound 250.

Bond wires 224 (only one shown) connect the contact pads 204 on the topsurface of the IC die 202 to leads 220.

As shown in FIG. 11, an elongate porous member 230 has a first end face232 and a second end face 236. Because the elongate member 230 isporous, air may pass through it from one end face 232 to the other 234.The air passing through the member 230 and also come into contact with atop surface or a sensing element 235, which in this embodiment is a flatsheet, that is mounted on the top surface of the sensor die 202 andbelow the elongate porous member 230. The elongate porous member 230 hasa mid portion 240 that is aligned with the sensor element 235. Theelongate porous member 230 may have a rectangular cross section and aflat longitudinally extending bottom face portion 245 (only a terminaledge is shown in FIG. 11) that engages the top surface of the IC die102. The first end face 232 of the elongate member 230 terminates flushwith one lateral side surface 251 of the mold compound block 250 and thesecond end 136 terminates flush with the opposite lateral side surface253 of the encapsulant block 250.

The elongate porous member 230 allows the ambient atmosphere (or othergases in some use environments) to come into contact with the sensorelement 235 on the top surface of the IC die 202. Different types ofsensor elements 235 are provided for different types of sensors, forexample humidity sensors and gas sensors.

In one embodiment the elongate porous member 230 is made from ePTFE,which is a stretched form of poly tetrafluoroethylene (“PTFE”) thatallows gases to pass through it while preventing liquid penetration. Inanother embodiment the elongate porous member 230 is made from porousceramic, which also has gas transmitting and liquid blocking properties.The manner of mounting the elongate porous members 230 on respectivedies 202 may be the same as described above for the tubular members 130.

An alternative structure for mounting elongate members, e.g., 130, 180,230, on dies, e.g. 102, 202, is illustrated in FIG. 13. In FIG. 13,tubular members 192 are arranged in a tubular member array 190. In thisarray the tubular members 192 are connected at opposite ends thereof toa pair of rags 194, 196. The rails may include holes 198 or structureadapted to facilitate handling of the tubular member array 190. Suchtubular member arrays may be handled in the same manner as conventionalleadframe inserts and enable mounting of multiple tubular members on aleadframe strip at the same time. The rails are trimmed off duringsingulation of the associated molded slab to form individual IC packages150, FIGS. 4 and 5. Although an elongate tubular member 170 having acircular cross section is illustrated in FIG. 13, a similar elongatemember array could be formed with any of the elongate member geometriccross sectional configurations and material types, e.g. tubular orporous, disclosed herein

A flowchart illustrating a method of making an integrated circuitpackage is shown in FIG. 14. The method includes as shown at block 301,attaching to an IC die mounted on a leadframe an elongate member that isadapted to transmit gas to a top surface of the IC die. The method alsoincludes, as shown at block 302, encapsulating the IC die, elongatemember and leadframe in mold compound in a manner that leaves surfaceportions of a die pad and leads of the leadframe and end portions of theelongate member exposed.

FIG. 15 is a flow diagram of a method of determining the value of aparameter of gas in a local environment with an encapsulated integratedcircuit sensor assembly. The method includes, as shown at block 310,passing gas from the local environment to a sensing element inside theencapsulated sensor assembly through an elongate member in fluidcommunication with the local environment.

Example embodiments of integrated circuit sensor packages and associatedmethods of making and using such integrated circuit sensor packages aredescribed in detain herein. Alternative embodiments of such integratedcircuit sensor packages and associated methods will occur to thoseskilled in the art after reading this disclosure. It is intended thatthe language of the claims be broadly construed to cover suchalternative embodiments, except as limited by the prior art.

What is claimed is:
 1. An integrated circuit (“IC”) package comprising:an IC die having a top surface and a bottom surface; an elongate memberhaving opposite first and second end portions and a mid portion, saidmid portion engaging said top surface of said IC die; and an encapsulantblock having a top surface, a bottom surface and opposite first andsecond lateral side faces, said encapsulant block encapsulating said ICdie and said elongate member with at least one of said first and secondend portions of said elongate member exposed; said IC die comprising asensor die having a sensing element on said top surface thereof, saidelongate member being constructed and arranged to transmit gastherethrough to said sensing element; said first and second end portionsof said elongate member being exposed at opposite lateral side surfacesof said encapsulant block; said elongate member being one of: a tubularmember, with at least one hole in said mid portion thereof that isconstructed from at least one of: carbon-nylon composite, epoxy resinand fluorine-containing rubber; and a porous member adapted to transmitgas therethrough and constructed from at least one ofpolytetrafluoroethylene (“PTFE”) and porous ceramic; and a leadframehaving a die pad and a plurality of leads, said IC die bottom surfacebeing attached to said die pad, said die pad and said leads beingexposed at said bottom surface of said encapsulant block wherein said ICdie comprises a plurality of electrical contact pads on at least oneexterior surface thereof that are wire bonded to at least one of saidplurality of leadframe leads.
 2. A method of making an integratedcircuit (“IC”) package comprising: attaching to an IC die mounted on aleadframe an elongate member that is adapted to transmit gas to a topsurface of the IC die; and encapsulating the IC die, elongate member andleadframe in mold compound in a manner that leaves surface portions of adie pad and leads of the leadframe and end portions of the elongatemember exposed.
 3. The method of claim 2 wherein said attachingcomprises attaching a plurality of elongate members to a plurality ofintegrated circuit dies mounted on a plurality of leadframes on aleadframe strip, wherein said encapsulating comprises encapsulating saidplurality of dies and said plurality of elongate members in a singleslab of encapsulant.
 4. The method of claim 3 further comprisingsingulating the single slab of encapsulant and the leadframe strip andthe elongate members so as to provide a plurality of IC packages eachhaving an elongate member mounted on an IC die mounted on a leadframeand encapsulated in an encapsulant block with opposite ends of theelongate member exposed through opposite lateral side faces of theencapsulant block.
 5. The method of claim 2 wherein said attachingcomprises attaching a tubular member.
 6. The method of claim 5 whereinsaid attaching further comprises: forming a hole at a mid portion of thetubular member; placing the portion of the tubular member with the holetherein in contact with a sensor element surface of the IC die; andproviding a vacuum in the tubular member to hold the tubular member inengagement with the IC die.
 7. The method of claim 5 wherein saidattaching comprises attaching the tubular member to the IC die with atleast one of solder and an adhesive compound.
 8. The method of claim 7wherein said attaching comprises attaching a porous member.
 9. Themethod of claim 8 wherein attaching a porous member comprises attachinga porous member with a generally rectangular cross section.
 10. Anintegrated circuit (“IC”) package comprising: an IC die having a topsurface and a bottom surface; an elongate member having opposite firstand second end portions and a mid portion, said mid portion positionedproximate said top surface of said IC die; an encapsulant block having atop surface, a bottom surface and opposite first and second lateral sidefaces, said encapsulant block encapsulating said IC die and saidelongate member with at least one of said first and second end portionsof said elongate member exposed; and a leadframe having a die pad and aplurality of leads, said IC die bottom surface being attached to saiddie pad, said die pad and said leads being exposed at said bottomsurface of said encapsulant block, wherein said IC die comprises aplurality of electrical contact pads on at least one exterior surfacethereof that are wire bonded to at least one of said plurality ofleadframe leads.
 11. The IC package of claim 10, said IC die comprisinga sensor die having a sensing element on said top surface thereof, saidelongate member being constructed and arranged to transmit gas therethrough to said sensing element.
 12. The IC package of claim 10 whereinboth of said first and second end portions of said elongate member areexposed at opposite lateral side surfaces of said encapsulant block. 13.The IC package of claim 10 wherein said elongate member is a tubularmember.
 14. The IC package of claim 13 wherein said tubular member hasat least one hole in said mid portion thereof.
 15. The IC package ofclaim 14 wherein said tubular member is constructed from at least oneof: carbon-nylon composite, epoxy resin and fluorine-containing rubber.16. The IC package of claim 13 wherein said tubular member defines afluid passage extending between said first and second end portionsthereof.
 17. The IC package of claim 10 wherein said elongate member isa porous member adapted to transmit gas there through.
 18. The ICpackage of claim 17 wherein said porous member is constructed ofpolytetrafluoroethylene (“PTFE”).
 19. The IC package of claim 10 whereinsaid encapsulant block is composed of mold compound.